Polar molecules have higher boiling and melting points compared to non-polar molecules due to the nature of their intermolecular forces. Polar molecules possess a permanent dipole moment, which means they have a positive end and a negative end. This polarity leads to stronger intermolecular forces known as dipole-dipole interactions.
In contrast, non-polar molecules do not have a permanent dipole moment. The intermolecular forces in non-polar molecules are primarily London dispersion forces, which are weaker than dipole-dipole interactions. London dispersion forces are temporary and arise due to the movement of electrons, creating temporary dipoles.
The stronger dipole-dipole interactions in polar molecules require more energy to break, resulting in higher boiling and melting points. For example, water (H2O) is a polar molecule with strong hydrogen bonding, a type of dipole-dipole interaction, which gives it a high boiling point of 100°C. On the other hand, methane (CH4), a non-polar molecule, has weaker London dispersion forces and a much lower boiling point of -161.5°C.
In summary, the higher boiling and melting points of polar molecules are due to the stronger intermolecular forces they experience compared to non-polar molecules.